This lack of discussion of civil rights issues at the hearing was glaring, but it may be in line with DeVos’ advocacy of school vouchers and other school choice programs in her home state of Michigan. As Kimberly Quick, a policy associate at the Century Foundation, notes, “Both historically and currently, voucher programs have served as a means for wealthier and white families to flee an increasingly diverse public school system, moving into largely unaccountable private schools that can exclude students based on a number of factors.”

And an increasing body of research suggests these concerns should not be isolated to vouchers, but to school choice programs of all kinds: Nationwide, school choice programs, such as charter schools and open enrollment options, have pushed more low-income minority students into even more racially segregated schools.

A 2010 study from the UCLA Civil Rights Project, for example, examined data from 40 states, the District of Columbia, and several dozen metropolitan areas. It found that 70 percent of black charter school students attended schools with 90 to 100 percent minority populations—double the percentage of intensely segregated black students in traditional public schools.

This increased segregation did not only apply to black students. The study also found that higher percentages of charter school students of every race attended more 50-to-100 percent minority student schools or 90-to-100 percent minority student schools than did their same-race peers in traditional public schools.

Other state-based studies in North Carolina, Pennsylvania, and Texas have also found that charter schools are deepening segregation, though a few city-based studies have shown contradictory results. Less academic literature exists on the impact of vouchers on school segregation.

“We don’t have a problem with charter schools, but we do have a problem with massive segregation.”

“Research shows that free-market school choice, without diversity as a stated goal of a program, tends to exacerbate segregation and inequality in schools,” says Halley Potter, a former charter school teacher and co-author of A Smarter Charter: Finding What Works for Charter Schools and Public Education. “The expansion of vouchers is particularly worrisome because of many private schools’ ability to pick and choose students based on academics, behavior, or even religion or sexuality.”

To show how school choice may be exacerbating school segregation, CityLab mapped charter school data from two communities—the Twin Cities of Minneapolis and St. Paul, Minnesota, and Charlotte, North Carolina—that were once lauded for their desegregation efforts.

Taking enrollment 2014-2015 data from the greater Twin Cities region’s charter schools, provided by the Institute on Metropolitan Opportunity, and underlaying it with the 2014 Census data, it becomes clear that these charter schools are recreating the neighborhood segregation patterns that previous desegregation efforts successfully counteracted.

Scrolling over the charter schools located in the intensely white outer ring suburbs of the map, you can see their student populations are also nearly all white. In majority non-white urban areas, the charter schools feature almost completely non-white populations. These charter schools are far less integrated than their peer public schools.

According to Will Stancil, an attorney and researcher at ‎the Institute on Metropolitan Opportunity at the University of Minnesota, as of the 2014-2015 school year, nearly 70 percent of students of color at charter schools in the Twin Cities were in completely segregated environments, compared to less than 20 percent at traditional schools. “The people that school choicedoesn’t reach are those whose parents are overwhelmed, who have no time to shop around,” he says. “Of course, those are the kids we should be helping, but in a consumer-oriented system you will never cater to them.”

The story is similar in North Carolina, where researchers in 2015 found that most white parents prefer sending their kids to schools that are no more than twenty percent black—and they use charter schools to make this choice. In grades 4-8, for example, Duke University researchers found that over the last fifteen years, North Carolina’s public school population became 11 percent less white (down to 53 percent), while its charter school population grew more white (up to 62.2 percent).

Mapping 2015 charter school data in the greater Charlotte area, you can see how these parent choices play out. Schools with student populations that are almost completely black (and sometimes Hispanic) cluster in the largely black urban core. Those in the inner-ring and outer-ring suburbs feature majority or almost exclusively white student populations. (Note: UNC Charlotte sociology professor Roslyn Mickelson provided CityLab with this data, but could not confirm whether Charlotte-area charter schools themselves are measurably more segregated than nearby public schools).

Eve Ewing, a sociologist of race and education at the University of Chicago School of Social Service Administration, argues such stratification is built into the design of many school choice programs. "The notion of ‘choice’ suggests that all options are on the table for all parents,” says Ewing, ”but when resources like transportation, childcare, and information access are unequally distributed, the choices on the table are in fact very constrained."

The Twin Cities and Charlotte examples also suggest that deregulated school operators, not just parents, may be helping drive the disparities in parents’ access to choices. In Minnesota, charter schools are not required by state law to take any action to reduce segregation. Similarly, North Carolina state law allows families to choose any charter in the state, as long as they can provide their own transportation. It can be far more difficult for non-affluent families to send their kids to charter schools in the wealthier parts of town: In the greater Charlotte-area charter schools mapped above, for example, only four of the twenty-one majority white and Asian charter schools provided free transportation, whereas seven of the fifteen majority black and Latino charter schools did so.

Some policy experts say school choice programs must take active steps to ensure they do not engineer district-level segregation. “In order for school choice to promote integration, diversity must be built into the design of the program,” says Potter. She points to Cambridge, Massachusetts, where “students are assigned to schools based on their families' ranked choices,” she says, and a system is in place to “make sure that all schools roughly reflect the diversity of the district.”

Charter school advocates observe that DeVos, or any Education Secretary, would have a limited ability to influence school diversity. In a statement, Vanessa Descalzi of the National Alliance for Public Charter Schools points out that “[c]harter schools are public schools and therefore, subject to the same federal requirements on integration as all other public schools. The Every Student Succeeds Act ensures important decisions about education, including the expansion and oversight of charter schools, remain firmly in the hands of states—the Secretary of Education has surprisingly little influence in those matters.”

For civil rights advocates, however, the concern is that DeVos’ extremely deregulated vision of school choice will exacerbate existing trends. “We don’t have a problem with charter schools, but we do have a problem with massive segregation,” says Yusef Mgeni, vice-president of the St. Paul NAACP and a former school administrator. “Public schools take anyone who walks off the sidewalk, but charters here will say, ‘We would love to take your child in, but he’s just not a good fit.’ DeVos has said her priorities are charters, vouchers, and choice … so people here are fastening their seat belts. We will be in for a rough ride.”